1. Field of the Invention
The present invention relates to a semiconductor photoelectric conversion device which has a photo-transistor structure.
2. Description of the Prior Art
Heretofore there has been proposed, as a semiconductor photoelectric conversion device of the photo-transistor structure, a semiconductor photoelectric conversion device of a vertical NPN (or PNP) type photo-transistor structure such that a single-crystal semiconductor substrate of a first conductivity type and serving as a collector region has formed therein on the side of the major surface thereof a single-crystal semiconductor region of a second conductivity type reverse from the first one and serving as a base region and the single crystal semiconductor region has formed therein a single-crystal semiconductor region of the first conductivity type and serving as an emitter region.
With such a conventional photoelectric conversion device, when it is irradiated by light, photo carriers are created at the boundary between the single-crystal semiconductor region acting as the base region and the single-crystal semiconductor region acting as the emitter region or in the vicinity of the abovesaid boundary, and the photo carriers are injected into the single-crystal semiconductor region acting as the base region, thereby obtaining multiplied photocurrent to perform photoelectric conversion.
In this case, a bias source is connected between the single-crystal semiconductor substrate as the collector region and the single-crystal semiconductor region as the emitter region but since the single-crystal semiconductor substrate as the collector region and the single-crystal semiconductor region as the base region are both formed of a single-crystal semiconductor, this prior art photoelectric conversion device has the advantages of high withstand voltage against the bias source and little internal leakage of photocurrent.
In the conventional photoelectric conversion device, however, the photo carrier generating efficiency is low partly because the photo carriers are generated at the boundary between the single-crystal semiconductor region as the base region and the single-crystal semiconductor region as the emitter region or in the vicinity of the abovesaid boundary, and partly because the region for generating the photo carriers is very small in thickness and is formed of a single-crystal semiconductor of small light absorption coefficient.
Accordingly, the abovesaid photoelectric conversion device is low in photoelectric conversion efficiency
Further since the photo carriers are created at the boundary between the single-crystal semiconductor region as the base region and the single-crystal semiconductor region as the emitter region or in the neighborhood of the boundary, since the single-crystal semiconductor region as the base region is formed in the single-crystal semiconductor substrate, and since the single-crystal semiconductor region as the emitter region is formed in the single-crystal semiconductor region as the base region, the conventional photoelectric conversion device performs photoelectric conversion only for light of a wavelength specified by the kind of semiconductor used for the single-crystal semiconductor substrate.
Therefore, the prior art photoelectric conversion device possesses the drawback that it has no photoelectric converting function for desired light, for example, visible light.
Further, according to the conventional photoelectric conversion device, the single-crystal semiconductor region as the emitter region is formed in the single-crystal semiconductor region as the base region, and the single-crystal semiconductor region as the base region is formed in the single-crystal semiconductor substrate, so that the single-crystal semiconductor region as the base region is formed of a single-crystal semiconductor of the kind determined by a single-crystal semiconductor of the kind or energy band determined by the kind of the single-crystal semiconductor forming the single-crystal semiconductor substrate. Consequently, the semiconductor region as the emitter region cannot be so formed as not to impose an appreciable loss on the light for generating the photo carriers is the aforesaid photo carrier generating region.
Therefore, the conventional photoelectric conversion device has the defect of low photoelectric conversion efficiency.
Moroever, there has also been proposed such a photoelectric conversion device that is entirely formed of a non-single-crystal semiconductor, including semiconductor regions as the collector region and as the base region.
With such a photoelectric conversion device, however, since the semiconductor regions as the collector region and as the base region are both formed on the non-single-crystal semiconductor, the withstand voltage against the bias source during operation of the device is far lower than the withstand voltage in the case of the aforesaid conventional photoelectric conversion device in which the semiconductor regions as the collector region and as the base region are formed of the single-crystal semiconductor, and leakage of photocurrent is large.
For the abovesaid reasons, the photoelectric conversion device employing the non-single-crystal semiconductor is difficult to put to practical use.